The North Branch of the Potomac River initially heads west from its source at the Fairfax Stone before curving north and then generally flowing east toward Chesapeake Bay. For this reason, the Stone is only a county corner of West Virginia counties rather than part of the state's border with Maryland, an issue that was only resolved when the Supreme Court ruled against Maryland in 1910 in Maryland v. West Virginia, determining that Maryland would only go westward up the Potomac far enough to meet a point where a line north from the Fairfax Stone would cross that branch of the Potomac.[6] Until the ruling, the boundary of Maryland was indeterminate. West Virginia counties—Tucker County and Preston County— share the boundary marked by the Fairfax Stone (West Virginia having seceded from Virginia during the American Civil War).

The original Fairfax Stone, in accordance with common surveying practices of the era[citation needed], was most likely simply a natural, unmarked rock selected from among the outcroppings in the area. Legal boundary disputes between Maryland and Virginia caused the latter to relocate the stone in 1833 after the site had been lost to memory.[7] The stone was still intact in 1859 when one Lieutenant Melcher found it again and reran the "Fairfax Line" on behalf of the two states. The Stone was gone by 1909, however, having been carried away by vandals.[7] There have been six Fairfax Stones, one replacing the next because of weather or graffiti. The current stone is a six-ton rock with a flat face, on which is inlaid a historical inscription of the stone's significance. Next to it is the 1910 stone.[8] The present Fairfax Stone was dedicated on October 5, 1957.[9]